diff --git a/docs/auth/google/gcp-iap-auth.md b/docs/auth/google/gcp-iap-auth.md
index 836abd4623..3c2cf68872 100644
--- a/docs/auth/google/gcp-iap-auth.md
+++ b/docs/auth/google/gcp-iap-auth.md
@@ -1,6 +1,6 @@
 ---
 id: provider
-title: Google Identity Aware Proxy Provider
+title: Google Identity-Aware Proxy Provider
 sidebar_label: Google IAP
 # prettier-ignore
 description: Adding Google Identity-Aware Proxy as an authentication provider in Backstage
@@ -12,103 +12,76 @@ Backstage allows offloading the responsibility of authenticating users to the
 Google HTTPS Load Balancer & [IAP](https://cloud.google.com/iap), leveraging the
 authentication support on the latter.
 
-This tutorial shows how to use authentication on an ALB sitting in front of
+This tutorial shows how to use authentication on an IAP sitting in front of
 Backstage.
 
 It is assumed an IAP is already serving traffic in front of a Backstage instance
 configured to serve the frontend app from the backend.
 
-## Infrastructure setup
+## Frontend Changes
 
-## Backstage changes
-
-### Frontend
-
-The Backstage App needs a `SignInPage` to be configured. When using IAP Proxy
+The Backstage app needs a `SignInPage` to be configured. When using IAP Proxy
 authentication Backstage will only be loaded once the user has successfully
 authenticated; we won't need to display a sign-in page as such, however we will
-need to create a dummy `SignInPage` component that can decode and refresh the
-token.
+need to create a dummy `SignInPage` component that can fetch the token and other
+information from the backend.
 
-- edit `packages/app/src/App.tsx`
-- import the following two additional definitions from `@backstage/core`:
-  `useApi`, `configApiRef`; these will be used to check whether Backstage is
-  running locally or behind an ALB
-- add the following definition just before the app is created
-  (`const app = createApp`):
+Create a sign-in page component in your app, for example in
+`packages/app/src/components/SignInPage.tsx`.
 
-```ts
-const refreshToken = async ({ props, discoveryApiConfig, config }) => {
-  const baseUrl = await discoveryApiConfig.getBaseUrl('auth');
-  const shouldAuth = !!config.getOptionalConfig('auth.providers.gcp-iap');
+```tsx
+import { GcpIapIdentity } from '@backstage/core-app-api';
+import { ErrorPanel, Progress } from '@backstage/core-components';
+import {
+  discoveryApiRef,
+  fetchApiRef,
+  SignInPageProps,
+  useApi,
+} from '@backstage/core-plugin-api';
+import { ResponseError } from '@backstage/errors';
+import React from 'react';
+import { useAsync } from 'react-use';
 
-  if (!shouldAuth) {
-    props.onResult({
-      userId: 'guest',
-      profile: {
-        email: 'guest@example.com',
-        displayName: 'Guest',
-        picture: '',
-      },
-    });
-    return;
-  }
+export const GcpIapSignInPage = (props: SignInPageProps) => {
+  const discovery = useApi(discoveryApiRef);
+  const { fetch } = useApi(fetchApiRef);
 
-  try {
-    const request = await fetch(`${baseUrl}/gcp-iap/refresh`, {
-      headers: {
-        'x-requested-with': 'XMLHttpRequest',
-      },
+  const { loading, error } = useAsync(async () => {
+    const base = await discovery.getBaseUrl('auth');
+    const response = await fetch(`${base}/gcp-iap/refresh`, {
+      headers: { 'x-requested-with': 'XMLHttpRequest' },
       credentials: 'include',
     });
-    const data = await request.json();
+    if (!response.ok) {
+      throw await ResponseError.fromResponse(response);
+    }
+    props.onSignInSuccess(GcpIapIdentity.fromResponse(await response.json()));
+  }, []);
 
-    props.onResult({
-      userId: data.backstageIdentity.id ?? 'nouser@ms.at',
-      profile: data.profile ?? 'nouser@ms.at',
-    });
-  } catch (e) {
-    props.onResult({
-      userId: 'guest',
-      profile: {
-        email: 'guest@example.com',
-        displayName: 'Guest',
-        picture: '',
-      },
-    });
-  }
-};
-
-const DummySignInComponent: any = (props: any) => {
-  try {
-    const config = useApi(configApiRef);
-    const discoveryApiConfig = useApi(discoveryApiRef);
-    refreshToken({ props, discoveryApiConfig, config });
-    return <div />;
-  } catch (err) {
-    return <div>{err.message}</div>;
-  }
+  if (loading) return <Progress />;
+  if (error) return <ErrorPanel error={error} />;
+  return null;
 };
 ```
 
-### Backend
+Pass this sign in page to your `createApp` function, in
+`packages/app/src/App.tsx`.
 
-When using ALB auth it is not possible to leverage the built-in auth config
-discovery mechanism implemented in the app created by default; bespoke logic
-needs to be implemented.
+```diff
++import { GcpIapSignInPage } from './components/SignInPage';
 
-- Replace the content of `packages/backend/plugin/auth.ts` with the below
+ const app = createApp({
+   components: {
++    SignInPage: GcpIapSignInPage
+```
+
+## Backend Changes
+
+- Add a `providerFactories` entry to the router in
+  `packages/backend/plugin/auth.ts`.
 
 ```ts
-// imports are relative - as this was tested out in repo directly
-import { createGcpIAPProvider } from './../providers/gcp-iap/provider';
-import { Router } from 'express';
-import { PluginEnvironment } from '../types';
-import {
-  createRouter,
-  AuthResponse,
-  AuthProviderFactoryOptions,
-} from '@backstage/plugin-auth-backend';
+import { createGcpIapProvider } from '@backstage/plugin-auth-backend';
 
 export default async function createPlugin({
   logger,
@@ -116,48 +89,49 @@ export default async function createPlugin({
   config,
   discovery,
 }: PluginEnvironment): Promise<Router> {
-  const identityResolver = (payload: any): Promise<AuthResponse<any>> => {
-    return Promise.resolve({
-      providerInfo: {},
-      profile: {
-        email: payload.email,
-        displayName: payload.name,
-        picture: payload.picture,
-      },
-      backstageIdentity: {
-        id: payload.email,
-      },
-    });
-  };
   return await createRouter({
     logger,
     config,
     database,
     discovery,
     providerFactories: {
-      'gcp-iap': (options: AuthProviderFactoryOptions) => {
-        return createGcpIAPProvider({ ...options, identityResolver })({
-          ...options,
-          identityResolver,
-        });
-      },
+      'gcp-iap': createGcpIapProvider({
+        // Replace the auth handler if you want to customize the returned user
+        // profile info (can be left out; default implementation shown below
+        // which only returns the email.
+        async authHandler({ iapToken }) {
+          return { profile: { email: iapToken.email } };
+        },
+        signIn: {
+          // You need to supply an identity resolver, that takes the profile
+          // and the IAP token and produces the Backstage token with the
+          // relevant user info.
+          async resolver({ profile, result: { iapToken } }, ctx) {
+            // Somehow compute the Backstage token claims, just some dummy code
+            // shown here, but you may want to query your LDAP server, or
+            // GSuite or similar, based on the IAP token sub/email claims
+            const id = `user:default/${iapToken.email.split('@')[0]}`;
+            const fullEnt = ['group:default/team-name'];
+            const token = await ctx.tokenIssuer.issueToken({
+              claims: { sub: id, ent: fullEnt },
+            });
+            return { id, token };
+          },
+        },
+      }),
     },
   });
 }
 ```
 
-### Configuration
+## Configuration
 
-Use the following `auth` configuration when running Backstage on AWS:
+Use the following `auth` configuration:
 
 ```yaml
 auth:
   providers:
     gcp-iap:
-      audience: '/projects/0123456/global/backendServices/1242345678765434567'
+      audience:
+        '/projects/<project number>/global/backendServices/<backend service id>'
 ```
-
-## Conclusion
-
-Once it's deployed, after going through the AAD authentication flow, Backstage
-should display the AAD user details.
diff --git a/packages/core-app-api/api-report.md b/packages/core-app-api/api-report.md
index f94979f975..ece34959de 100644
--- a/packages/core-app-api/api-report.md
+++ b/packages/core-app-api/api-report.md
@@ -21,7 +21,9 @@ import { AuthProviderInfo } from '@backstage/core-plugin-api';
 import { AuthRequestOptions } from '@backstage/core-plugin-api';
 import { BackstageIdentity } from '@backstage/core-plugin-api';
 import { BackstageIdentityApi } from '@backstage/core-plugin-api';
+import { BackstageIdentityResponse } from '@backstage/core-plugin-api';
 import { BackstagePlugin } from '@backstage/core-plugin-api';
+import { BackstageUserIdentity } from '@backstage/core-plugin-api';
 import { bitbucketAuthApiRef } from '@backstage/core-plugin-api';
 import { ComponentType } from 'react';
 import { Config } from '@backstage/config';
@@ -388,6 +390,41 @@ export type FlatRoutesProps = {
   children: ReactNode;
 };
 
+// @public
+export class GcpIapIdentity implements IdentityApi {
+  constructor(session: GcpIapSession);
+  static fromResponse(data: unknown): GcpIapIdentity;
+  // (undocumented)
+  getBackstageIdentity(): Promise<BackstageUserIdentity>;
+  // (undocumented)
+  getCredentials(): Promise<{
+    token?: string | undefined;
+  }>;
+  // (undocumented)
+  getIdToken(): Promise<string | undefined>;
+  // (undocumented)
+  getProfile(): ProfileInfo;
+  // (undocumented)
+  getProfileInfo(): Promise<ProfileInfo>;
+  // (undocumented)
+  getUserId(): string;
+  // (undocumented)
+  signOut(): Promise<void>;
+}
+
+// @public
+export type GcpIapSession = {
+  providerInfo: {
+    iapToken: {
+      sub: string;
+      email: string;
+      [key: string]: unknown;
+    };
+  };
+  profile: ProfileInfo;
+  backstageIdentity: BackstageIdentityResponse;
+};
+
 // @public
 export class GithubAuth implements OAuthApi, SessionApi {
   // (undocumented)
diff --git a/packages/core-app-api/src/apis/implementations/auth/gcp-iap/GcpIapIdentity.ts b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/GcpIapIdentity.ts
new file mode 100644
index 0000000000..0df14e1d99
--- /dev/null
+++ b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/GcpIapIdentity.ts
@@ -0,0 +1,74 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {
+  BackstageUserIdentity,
+  IdentityApi,
+  ProfileInfo,
+} from '@backstage/core-plugin-api';
+import { GcpIapSession, gcpIapSessionSchema } from './types';
+
+/**
+ * An identity API based on a Google Identity-Aware Proxy auth response.
+ *
+ * @public
+ */
+export class GcpIapIdentity implements IdentityApi {
+  /**
+   * Creates an identity instance based on the auth-backend API response.
+   *
+   * @param data - The raw JSON response from the auth-backend.
+   */
+  static fromResponse(data: unknown): GcpIapIdentity {
+    const parsed = gcpIapSessionSchema.parse(data);
+    return new GcpIapIdentity(parsed);
+  }
+
+  constructor(private readonly session: GcpIapSession) {}
+
+  /** {@inheritdoc @backstage/core-plugin-api#IdentityApi.getUserId} */
+  getUserId(): string {
+    return this.session.backstageIdentity.id;
+  }
+
+  /** {@inheritdoc @backstage/core-plugin-api#IdentityApi.getIdToken} */
+  async getIdToken(): Promise<string | undefined> {
+    return this.session.backstageIdentity.token;
+  }
+
+  /** {@inheritdoc @backstage/core-plugin-api#IdentityApi.getProfile} */
+  getProfile(): ProfileInfo {
+    return this.session.profile;
+  }
+
+  /** {@inheritdoc @backstage/core-plugin-api#IdentityApi.getProfileInfo} */
+  async getProfileInfo(): Promise<ProfileInfo> {
+    return this.session.profile;
+  }
+
+  /** {@inheritdoc @backstage/core-plugin-api#IdentityApi.getBackstageIdentity} */
+  async getBackstageIdentity(): Promise<BackstageUserIdentity> {
+    return this.session.backstageIdentity.identity;
+  }
+
+  /** {@inheritdoc @backstage/core-plugin-api#IdentityApi.getCredentials} */
+  async getCredentials(): Promise<{ token?: string | undefined }> {
+    return { token: this.session.backstageIdentity.token };
+  }
+
+  /** {@inheritdoc @backstage/core-plugin-api#IdentityApi.signOut} */
+  async signOut(): Promise<void> {}
+}
diff --git a/packages/core-app-api/src/apis/implementations/auth/gcp-iap/index.ts b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/index.ts
new file mode 100644
index 0000000000..8133061f20
--- /dev/null
+++ b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/index.ts
@@ -0,0 +1,18 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export { GcpIapIdentity } from './GcpIapIdentity';
+export type { GcpIapSession } from './types';
diff --git a/packages/core-app-api/src/apis/implementations/auth/gcp-iap/types.test.ts b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/types.test.ts
new file mode 100644
index 0000000000..cb185103e2
--- /dev/null
+++ b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/types.test.ts
@@ -0,0 +1,50 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { TypeOf } from 'zod';
+import { GcpIapSession, gcpIapSessionSchema } from './types';
+
+describe('types', () => {
+  const responseData: GcpIapSession = {
+    providerInfo: {
+      iapToken: {
+        sub: 's',
+        email: 'e',
+        other: 7,
+      },
+    },
+    profile: {
+      email: 'e',
+      displayName: 'd',
+      picture: 'p',
+    },
+    backstageIdentity: {
+      id: 'i',
+      token: 't',
+      identity: {
+        type: 'user',
+        userEntityRef: 'ue',
+        ownershipEntityRefs: ['oe'],
+      },
+    },
+  };
+
+  it('has a compatible schema type', () => {
+    function f(_b: TypeOf<typeof gcpIapSessionSchema>) {}
+    f(responseData); // no tsc errors
+    expect(gcpIapSessionSchema.parse(responseData)).toEqual(responseData);
+  });
+});
diff --git a/packages/core-app-api/src/apis/implementations/auth/gcp-iap/types.ts b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/types.ts
new file mode 100644
index 0000000000..98c728785d
--- /dev/null
+++ b/packages/core-app-api/src/apis/implementations/auth/gcp-iap/types.ts
@@ -0,0 +1,63 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {
+  BackstageIdentityResponse,
+  ProfileInfo,
+} from '@backstage/core-plugin-api';
+import { z } from 'zod';
+
+export const gcpIapSessionSchema = z.object({
+  providerInfo: z.object({
+    iapToken: z
+      .object({
+        sub: z.string(),
+        email: z.string(),
+      })
+      .catchall(z.unknown()),
+  }),
+  profile: z.object({
+    email: z.string().optional(),
+    displayName: z.string().optional(),
+    picture: z.string().optional(),
+  }),
+  backstageIdentity: z.object({
+    id: z.string(),
+    token: z.string(),
+    identity: z.object({
+      type: z.literal('user'),
+      userEntityRef: z.string(),
+      ownershipEntityRefs: z.array(z.string()),
+    }),
+  }),
+});
+
+/**
+ * Session information for Google Identity-Aware Proxy auth.
+ *
+ * @public
+ */
+export type GcpIapSession = {
+  providerInfo: {
+    iapToken: {
+      sub: string;
+      email: string;
+      [key: string]: unknown;
+    };
+  };
+  profile: ProfileInfo;
+  backstageIdentity: BackstageIdentityResponse;
+};
diff --git a/packages/core-app-api/src/apis/implementations/auth/index.ts b/packages/core-app-api/src/apis/implementations/auth/index.ts
index 50333f07a0..c53c9b7c76 100644
--- a/packages/core-app-api/src/apis/implementations/auth/index.ts
+++ b/packages/core-app-api/src/apis/implementations/auth/index.ts
@@ -25,4 +25,5 @@ export * from './microsoft';
 export * from './onelogin';
 export * from './bitbucket';
 export * from './atlassian';
+export * from './gcp-iap';
 export type { OAuthApiCreateOptions, AuthApiCreateOptions } from './types';
diff --git a/plugins/auth-backend/api-report.md b/plugins/auth-backend/api-report.md
index af46d874df..ab8bd39a94 100644
--- a/plugins/auth-backend/api-report.md
+++ b/plugins/auth-backend/api-report.md
@@ -9,6 +9,7 @@ import { CatalogApi } from '@backstage/catalog-client';
 import { Config } from '@backstage/config';
 import { Entity } from '@backstage/catalog-model';
 import express from 'express';
+import { JsonValue } from '@backstage/types';
 import { JSONWebKey } from 'jose';
 import { Logger as Logger_2 } from 'winston';
 import { PluginDatabaseManager } from '@backstage/backend-common';
@@ -59,8 +60,8 @@ export type Auth0ProviderOptions = {
 };
 
 // @public
-export type AuthHandler<AuthResult> = (
-  input: AuthResult,
+export type AuthHandler<TAuthResult> = (
+  input: TAuthResult,
 ) => Promise<AuthHandlerResult>;
 
 // @public
@@ -249,6 +250,11 @@ export const createBitbucketProvider: (
   options?: BitbucketProviderOptions | undefined,
 ) => AuthProviderFactory;
 
+// @public
+export function createGcpIapProvider(
+  options: GcpIapProviderOptions,
+): AuthProviderFactory;
+
 // Warning: (ae-missing-release-tag) "createGithubProvider" is exported by the package, but it is missing a release tag (@alpha, @beta, @public, or @internal)
 //
 // @public (undocumented)
@@ -335,6 +341,26 @@ export const encodeState: (state: OAuthState) => string;
 // @public (undocumented)
 export const ensuresXRequestedWith: (req: express.Request) => boolean;
 
+// @public
+export type GcpIapProviderOptions = {
+  authHandler?: AuthHandler<GcpIapResult>;
+  signIn: {
+    resolver: SignInResolver<GcpIapResult>;
+  };
+};
+
+// @public
+export type GcpIapResult = {
+  iapToken: GcpIapTokenInfo;
+};
+
+// @public
+export type GcpIapTokenInfo = {
+  sub: string;
+  email: string;
+  [key: string]: JsonValue;
+};
+
 // Warning: (ae-forgotten-export) The symbol "TokenParams" needs to be exported by the entry point index.d.ts
 // Warning: (ae-missing-release-tag) "getEntityClaims" is exported by the package, but it is missing a release tag (@alpha, @beta, @public, or @internal)
 //
@@ -661,14 +687,14 @@ export type SamlProviderOptions = {
 };
 
 // @public
-export type SignInInfo<AuthResult> = {
+export type SignInInfo<TAuthResult> = {
   profile: ProfileInfo;
-  result: AuthResult;
+  result: TAuthResult;
 };
 
 // @public
-export type SignInResolver<AuthResult> = (
-  info: SignInInfo<AuthResult>,
+export type SignInResolver<TAuthResult> = (
+  info: SignInInfo<TAuthResult>,
   context: {
     tokenIssuer: TokenIssuer;
     catalogIdentityClient: CatalogIdentityClient;
diff --git a/plugins/auth-backend/package.json b/plugins/auth-backend/package.json
index bdc75f40e5..fa1fcd69cb 100644
--- a/plugins/auth-backend/package.json
+++ b/plugins/auth-backend/package.json
@@ -36,6 +36,7 @@
     "@backstage/config": "^0.1.11",
     "@backstage/errors": "^0.1.5",
     "@backstage/test-utils": "^0.2.1",
+    "@backstage/types": "^0.1.1",
     "@google-cloud/firestore": "^4.15.1",
     "@types/express": "^4.17.6",
     "@types/passport": "^1.0.3",
@@ -45,11 +46,8 @@
     "express": "^4.17.1",
     "express-promise-router": "^4.1.0",
     "express-session": "^1.17.1",
-<<<<<<< HEAD
-=======
     "fs-extra": "9.1.0",
->>>>>>> 4d5fd11228 (first minor cleanups)
-    "google-auth-library": "^7.2.0",
+    "google-auth-library": "^7.6.1",
     "helmet": "^4.0.0",
     "jose": "^1.27.1",
     "jwt-decode": "^3.1.0",
@@ -87,7 +85,8 @@
     "@types/passport-saml": "^1.1.3",
     "@types/passport-strategy": "^0.2.35",
     "@types/xml2js": "^0.4.7",
-    "msw": "^0.35.0"
+    "msw": "^0.35.0",
+    "supertest": "^6.1.3"
   },
   "files": [
     "dist",
diff --git a/plugins/auth-backend/src/providers/aws-alb/index.ts b/plugins/auth-backend/src/providers/aws-alb/index.ts
index 5f63c514a4..a8130b3575 100644
--- a/plugins/auth-backend/src/providers/aws-alb/index.ts
+++ b/plugins/auth-backend/src/providers/aws-alb/index.ts
@@ -13,5 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 export { createAwsAlbProvider } from './provider';
 export type { AwsAlbProviderOptions } from './provider';
diff --git a/plugins/auth-backend/src/providers/aws-alb/provider.test.ts b/plugins/auth-backend/src/providers/aws-alb/provider.test.ts
index 048128f942..fd5fe28505 100644
--- a/plugins/auth-backend/src/providers/aws-alb/provider.test.ts
+++ b/plugins/auth-backend/src/providers/aws-alb/provider.test.ts
@@ -18,7 +18,7 @@ import express from 'express';
 import { JWT } from 'jose';
 
 import {
-  ALB_ACCESSTOKEN_HEADER,
+  ALB_ACCESS_TOKEN_HEADER,
   ALB_JWT_HEADER,
   AwsAlbAuthProvider,
 } from './provider';
@@ -80,7 +80,7 @@ describe('AwsAlbAuthProvider', () => {
     header: jest.fn(name => {
       if (name === ALB_JWT_HEADER) {
         return mockJwt;
-      } else if (name === ALB_ACCESSTOKEN_HEADER) {
+      } else if (name === ALB_ACCESS_TOKEN_HEADER) {
         return mockAccessToken;
       }
       return undefined;
@@ -88,7 +88,7 @@ describe('AwsAlbAuthProvider', () => {
   } as unknown as express.Request;
   const mockRequestWithoutJwt = {
     header: jest.fn(name => {
-      if (name === ALB_ACCESSTOKEN_HEADER) {
+      if (name === ALB_ACCESS_TOKEN_HEADER) {
         return mockAccessToken;
       }
       return undefined;
diff --git a/plugins/auth-backend/src/providers/aws-alb/provider.ts b/plugins/auth-backend/src/providers/aws-alb/provider.ts
index 114bc9a204..4f05cd7827 100644
--- a/plugins/auth-backend/src/providers/aws-alb/provider.ts
+++ b/plugins/auth-backend/src/providers/aws-alb/provider.ts
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 import {
   AuthHandler,
   AuthProviderFactory,
@@ -35,7 +36,7 @@ import { AuthenticationError } from '@backstage/errors';
 import { prepareBackstageIdentityResponse } from '../prepareBackstageIdentityResponse';
 
 export const ALB_JWT_HEADER = 'x-amzn-oidc-data';
-export const ALB_ACCESSTOKEN_HEADER = 'x-amzn-oidc-accesstoken';
+export const ALB_ACCESS_TOKEN_HEADER = 'x-amzn-oidc-accesstoken';
 
 type Options = {
   region: string;
@@ -134,7 +135,7 @@ export class AwsAlbAuthProvider implements AuthProviderRouteHandlers {
 
   private async getResult(req: express.Request): Promise<AwsAlbResult> {
     const jwt = req.header(ALB_JWT_HEADER);
-    const accessToken = req.header(ALB_ACCESSTOKEN_HEADER);
+    const accessToken = req.header(ALB_ACCESS_TOKEN_HEADER);
 
     if (jwt === undefined) {
       throw new AuthenticationError(
@@ -144,7 +145,7 @@ export class AwsAlbAuthProvider implements AuthProviderRouteHandlers {
 
     if (accessToken === undefined) {
       throw new AuthenticationError(
-        `Missing ALB OIDC header: ${ALB_ACCESSTOKEN_HEADER}`,
+        `Missing ALB OIDC header: ${ALB_ACCESS_TOKEN_HEADER}`,
       );
     }
 
diff --git a/plugins/auth-backend/src/providers/gcp-iap/helpers.test.ts b/plugins/auth-backend/src/providers/gcp-iap/helpers.test.ts
new file mode 100644
index 0000000000..5063090442
--- /dev/null
+++ b/plugins/auth-backend/src/providers/gcp-iap/helpers.test.ts
@@ -0,0 +1,124 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { ConflictError } from '@backstage/errors';
+import { OAuth2Client } from 'google-auth-library';
+import { createTokenValidator, parseRequestToken } from './helpers';
+
+const validJwt =
+  'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImZvbyIsImlzcyI6ImZvbyJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.T2BNS4G-6RoiFnXc8Q8TiwdWzTpNitY8jcsGM3N3-Yo';
+
+beforeEach(() => {
+  jest.clearAllMocks();
+});
+
+describe('helpers', () => {
+  describe('createTokenValidator', () => {
+    it('runs the happy path', async () => {
+      const mockClient = {
+        getIapPublicKeys: async () => ({ pubkeys: '' }),
+        verifySignedJwtWithCertsAsync: async () => ({
+          getPayload: () => ({ sub: 's', email: 'e@mail.com' }),
+        }),
+      };
+      const validator = createTokenValidator(
+        'a',
+        mockClient as unknown as OAuth2Client,
+      );
+      await expect(validator(validJwt)).resolves.toMatchObject({
+        sub: 's',
+        email: 'e@mail.com',
+      });
+    });
+
+    it('throws if the client throws', async () => {
+      const mockClient = {
+        getIapPublicKeys: async () => {
+          throw new TypeError('bam');
+        },
+      };
+      const validator = createTokenValidator(
+        'a',
+        mockClient as unknown as OAuth2Client,
+      );
+      await expect(validator(validJwt)).rejects.toThrowError(TypeError);
+    });
+  });
+
+  describe('parseRequestToken', () => {
+    it('runs the happy path', async () => {
+      await expect(
+        parseRequestToken(
+          validJwt,
+          async () => ({ sub: 's', email: 'e@mail.com' } as any),
+        ),
+      ).resolves.toMatchObject({
+        iapToken: {
+          sub: 's',
+          email: 'e@mail.com',
+        },
+      });
+    });
+
+    it('rejects bad tokens', async () => {
+      await expect(
+        parseRequestToken(7, undefined as any),
+      ).rejects.toMatchObject({
+        name: 'AuthenticationError',
+        message: 'Missing Google IAP header: x-goog-iap-jwt-assertion',
+      });
+      await expect(
+        parseRequestToken(undefined, undefined as any),
+      ).rejects.toMatchObject({
+        name: 'AuthenticationError',
+        message: 'Missing Google IAP header: x-goog-iap-jwt-assertion',
+      });
+      await expect(
+        parseRequestToken('', undefined as any),
+      ).rejects.toMatchObject({
+        name: 'AuthenticationError',
+        message: 'Missing Google IAP header: x-goog-iap-jwt-assertion',
+      });
+    });
+
+    it('translates validator errors', async () => {
+      await expect(
+        parseRequestToken(validJwt, async () => {
+          throw new ConflictError('Ouch');
+        }),
+      ).rejects.toMatchObject({
+        name: 'AuthenticationError',
+        message: 'Google IAP token verification failed, ConflictError: Ouch',
+      });
+    });
+
+    it('rejects bad token payloads', async () => {
+      await expect(
+        parseRequestToken(validJwt, async () => undefined as any),
+      ).rejects.toMatchObject({
+        name: 'AuthenticationError',
+        message: 'Google IAP token had no payload',
+      });
+
+      await expect(
+        parseRequestToken(validJwt, async () => ({ sub: 'a' } as any)),
+      ).rejects.toMatchObject({
+        name: 'AuthenticationError',
+        message: 'Google IAP token payload had no sub or email claim',
+      });
+    });
+  });
+});
diff --git a/plugins/auth-backend/src/providers/gcp-iap/helpers.ts b/plugins/auth-backend/src/providers/gcp-iap/helpers.ts
new file mode 100644
index 0000000000..0bc4c34ecc
--- /dev/null
+++ b/plugins/auth-backend/src/providers/gcp-iap/helpers.ts
@@ -0,0 +1,82 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { AuthenticationError } from '@backstage/errors';
+import { OAuth2Client, TokenPayload } from 'google-auth-library';
+import { AuthHandler } from '../types';
+import { GcpIapResult, IAP_JWT_HEADER } from './types';
+
+export function createTokenValidator(
+  audience: string,
+  mockClient?: OAuth2Client,
+): (token: string) => Promise<TokenPayload> {
+  return async function tokenValidator(token) {
+    const client = mockClient ?? new OAuth2Client();
+
+    const response = await client.getIapPublicKeys();
+    const ticket = await client.verifySignedJwtWithCertsAsync(
+      token,
+      response.pubkeys,
+      audience,
+      ['https://cloud.google.com/iap'],
+    );
+
+    const payload = ticket.getPayload();
+    if (!payload) {
+      throw new TypeError('No payload');
+    }
+
+    return payload;
+  };
+}
+
+export async function parseRequestToken(
+  jwtToken: unknown,
+  tokenValidator: (token: string) => Promise<TokenPayload>,
+): Promise<GcpIapResult> {
+  if (typeof jwtToken !== 'string' || !jwtToken) {
+    throw new AuthenticationError(
+      `Missing Google IAP header: ${IAP_JWT_HEADER}`,
+    );
+  }
+
+  let payload: TokenPayload;
+  try {
+    payload = await tokenValidator(jwtToken);
+  } catch (e) {
+    throw new AuthenticationError(`Google IAP token verification failed, ${e}`);
+  }
+
+  if (!payload) {
+    throw new AuthenticationError('Google IAP token had no payload');
+  } else if (!payload.sub || !payload.email) {
+    throw new AuthenticationError(
+      'Google IAP token payload had no sub or email claim',
+    );
+  }
+
+  return {
+    iapToken: {
+      ...payload,
+      sub: payload.sub,
+      email: payload.email,
+    },
+  };
+}
+
+export const defaultAuthHandler: AuthHandler<GcpIapResult> = async ({
+  iapToken,
+}) => ({ profile: { email: iapToken.email } });
diff --git a/plugins/auth-backend/src/providers/gcp-iap/index.ts b/plugins/auth-backend/src/providers/gcp-iap/index.ts
index 634eb37a4a..fe5d178fcc 100644
--- a/plugins/auth-backend/src/providers/gcp-iap/index.ts
+++ b/plugins/auth-backend/src/providers/gcp-iap/index.ts
@@ -14,5 +14,9 @@
  * limitations under the License.
  */
 
-export { createGcpIAPProvider } from './provider';
-export type { GcpIAPProviderOptions } from './provider';
+export { createGcpIapProvider } from './provider';
+export type {
+  GcpIapProviderOptions,
+  GcpIapResult,
+  GcpIapTokenInfo,
+} from './types';
diff --git a/plugins/auth-backend/src/providers/gcp-iap/provider.test.ts b/plugins/auth-backend/src/providers/gcp-iap/provider.test.ts
index d2a70c043c..bb1ed5c79b 100644
--- a/plugins/auth-backend/src/providers/gcp-iap/provider.test.ts
+++ b/plugins/auth-backend/src/providers/gcp-iap/provider.test.ts
@@ -16,107 +16,61 @@
 
 import { getVoidLogger } from '@backstage/backend-common';
 import express from 'express';
-import { AuthResponse } from '../types';
-import { GcpIAPProvider } from './provider';
-
-jest.mock('google-auth-library');
-
-const identityResolutionCallbackMock = async (): Promise<AuthResponse<any>> => {
-  return {
-    backstageIdentity: {
-      id: 'foo',
-      idToken: '',
-    },
-    profile: {
-      displayName: 'Foo Bar',
-    },
-    providerInfo: {},
-  };
-};
-
-const identityResolutionCallbackRejectedMock = async (): Promise<
-  AuthResponse<any>
-> => {
-  throw new Error('failed');
-};
+import request from 'supertest';
+import { GcpIapProvider } from './provider';
 
 beforeEach(() => {
   jest.clearAllMocks();
 });
 
-describe('GcpIAPProvider', () => {
-  const catalogApi = {
-    /* eslint-disable-next-line @typescript-eslint/no-unused-vars */
-    addLocation: jest.fn(),
-    removeLocationById: jest.fn(),
-    getEntities: jest.fn(),
-    getOriginLocationByEntity: jest.fn(),
-    getLocationByEntity: jest.fn(),
-    getLocationById: jest.fn(),
-    removeEntityByUid: jest.fn(),
-    getEntityByName: jest.fn(),
-  };
+describe('GcpIapProvider', () => {
+  const authHandler = jest.fn();
+  const signInResolver = jest.fn();
+  const tokenValidator = jest.fn();
+  const logger = getVoidLogger();
 
-  const mockRequest = {
-    header: jest.fn(() => {
-      return 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImZvbyIsImlzcyI6ImZvbyJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.T2BNS4G-6RoiFnXc8Q8TiwdWzTpNitY8jcsGM3N3-Yo';
-    }),
-  } as unknown as express.Request;
-  const mockRequestWithoutJwt = {
-    header: jest.fn(() => {
-      return undefined;
-    }),
-  } as unknown as express.Request;
-  const mockResponse = {
-    end: jest.fn(),
-    header: () => jest.fn(),
-    json: jest.fn().mockReturnThis(),
-    status: jest.fn(),
-  } as unknown as express.Response;
-
-  describe('should transform to type OAuthResponse', () => {
-    it('when JWT is valid and identity is resolved successfully', async () => {
-      const provider = new GcpIAPProvider(getVoidLogger(), catalogApi, {
-        identityResolutionCallback: identityResolutionCallbackMock,
-        audience: 'foo',
-      });
-
-      await provider.refresh(mockRequest, mockResponse);
-
-      expect(mockResponse.json).toHaveBeenCalledWith({
-        backstageIdentity: {
-          id: 'foo',
-          idToken: '',
-        },
-        profile: {
-          displayName: 'Foo Bar',
-        },
-        providerInfo: {},
-      });
-    });
-  });
-  describe('should fail when', () => {
-    it('JWT is missing', async () => {
-      const provider = new GcpIAPProvider(getVoidLogger(), catalogApi, {
-        identityResolutionCallback: identityResolutionCallbackMock,
-        audience: 'foo',
-      });
-
-      await provider.refresh(mockRequestWithoutJwt, mockResponse);
-
-      expect(mockResponse.status).toHaveBeenCalledWith(401);
+  it('runs the happy path', async () => {
+    const provider = new GcpIapProvider({
+      authHandler,
+      signInResolver,
+      tokenValidator,
+      tokenIssuer: {} as any,
+      catalogIdentityClient: {} as any,
+      logger,
     });
 
-    it('identity resolution callback rejects', async () => {
-      const provider = new GcpIAPProvider(getVoidLogger(), catalogApi, {
-        identityResolutionCallback: identityResolutionCallbackRejectedMock,
-        audience: 'foo',
-      });
+    // { "sub": "user:default/me", "ent": ["group:default/home"] }
+    const backstageToken =
+      'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJ1c2VyOmRlZmF1bHQvbWUiLCJlbnQiOlsiZ3JvdXA6ZGVmYXVsdC9ob21lIl19.CbmAKzFErGmtsnpRxyPc7dHv7WEjb5lY6206YCzR_Rc';
+    const iapToken = { sub: 's', email: 'e@mail.com' };
 
-      await provider.refresh(mockRequest, mockResponse);
+    authHandler.mockResolvedValueOnce({ email: 'e@mail.com' });
+    signInResolver.mockResolvedValueOnce({ id: 'i', token: backstageToken });
+    tokenValidator.mockResolvedValueOnce(iapToken);
 
-      expect(mockResponse.status).toHaveBeenCalledWith(401);
-      expect(mockResponse.end).toHaveBeenCalledTimes(1);
+    const app = express();
+    app.use('/refresh', provider.refresh.bind(provider));
+
+    const response = await request(app)
+      .get('/refresh')
+      .set('x-goog-iap-jwt-assertion', 'token');
+
+    expect(response.status).toBe(200);
+    expect(response.get('content-type')).toBe(
+      'application/json; charset=utf-8',
+    );
+    expect(response.body).toEqual({
+      backstageIdentity: {
+        id: 'i',
+        idToken: backstageToken,
+        token: backstageToken,
+        identity: {
+          type: 'user',
+          userEntityRef: 'user:default/me',
+          ownershipEntityRefs: ['group:default/home'],
+        },
+      },
+      providerInfo: { iapToken },
     });
   });
 });
diff --git a/plugins/auth-backend/src/providers/gcp-iap/provider.ts b/plugins/auth-backend/src/providers/gcp-iap/provider.ts
index 33235083ca..9007fa24fe 100644
--- a/plugins/auth-backend/src/providers/gcp-iap/provider.ts
+++ b/plugins/auth-backend/src/providers/gcp-iap/provider.ts
@@ -14,111 +14,112 @@
  * limitations under the License.
  */
 
-import { CatalogApi } from '@backstage/catalog-client';
 import express from 'express';
-import { OAuth2Client } from 'google-auth-library';
+import { TokenPayload } from 'google-auth-library';
 import { Logger } from 'winston';
+import { TokenIssuer } from '../../identity/types';
+import { CatalogIdentityClient } from '../../lib/catalog';
+import { prepareBackstageIdentityResponse } from '../prepareBackstageIdentityResponse';
 import {
+  AuthHandler,
   AuthProviderFactory,
-  AuthProviderFactoryOptions,
   AuthProviderRouteHandlers,
-  ExperimentalIdentityResolver,
+  SignInResolver,
 } from '../types';
+import {
+  createTokenValidator,
+  defaultAuthHandler,
+  parseRequestToken,
+} from './helpers';
+import {
+  GcpIapProviderOptions,
+  GcpIapResponse,
+  GcpIapResult,
+  IAP_JWT_HEADER,
+} from './types';
 
-const IAP_JWT_HEADER = 'x-goog-iap-jwt-assertion';
+export class GcpIapProvider implements AuthProviderRouteHandlers {
+  private readonly authHandler: AuthHandler<GcpIapResult>;
+  private readonly signInResolver: SignInResolver<GcpIapResult>;
+  private readonly tokenValidator: (token: string) => Promise<TokenPayload>;
+  private readonly tokenIssuer: TokenIssuer;
+  private readonly catalogIdentityClient: CatalogIdentityClient;
+  private readonly logger: Logger;
 
-export type GcpIAPProviderOptions = {
-  audience: string;
-  identityResolutionCallback: ExperimentalIdentityResolver;
-};
-export class GcpIAPProvider implements AuthProviderRouteHandlers {
-  private logger: Logger;
-  private options: GcpIAPProviderOptions;
-  private readonly catalogClient: CatalogApi;
-
-  constructor(
-    logger: Logger,
-    catalogClient: CatalogApi,
-    options: GcpIAPProviderOptions,
-  ) {
-    this.logger = logger;
-    this.catalogClient = catalogClient;
-    this.options = options;
+  constructor(options: {
+    authHandler: AuthHandler<GcpIapResult>;
+    signInResolver: SignInResolver<GcpIapResult>;
+    tokenValidator: (token: string) => Promise<TokenPayload>;
+    tokenIssuer: TokenIssuer;
+    catalogIdentityClient: CatalogIdentityClient;
+    logger: Logger;
+  }) {
+    this.authHandler = options.authHandler;
+    this.signInResolver = options.signInResolver;
+    this.tokenValidator = options.tokenValidator;
+    this.tokenIssuer = options.tokenIssuer;
+    this.catalogIdentityClient = options.catalogIdentityClient;
+    this.logger = options.logger;
   }
 
-  frameHandler(): Promise<void> {
-    return Promise.resolve(undefined);
-  }
+  async start() {}
+
+  async frameHandler() {}
 
   async refresh(req: express.Request, res: express.Response): Promise<void> {
-    const expectedAudience = this.options.audience;
-    const jwtToken = req.header(IAP_JWT_HEADER);
-    if (jwtToken === undefined) {
-      res.status(401);
-      res.end();
-      return;
-    }
-    const oAuth2Client = new OAuth2Client();
-    const verify = async () => {
-      const response = await oAuth2Client.getIapPublicKeys();
-      const ticket = await oAuth2Client.verifySignedJwtWithCertsAsync(
-        jwtToken,
-        response.pubkeys,
-        expectedAudience,
-        ['https://cloud.google.com/iap'],
-      );
-      return ticket.getPayload();
+    const result = await parseRequestToken(
+      req.header(IAP_JWT_HEADER),
+      this.tokenValidator,
+    );
+
+    const { profile } = await this.authHandler(result);
+
+    const backstageIdentity = await this.signInResolver(
+      { profile, result },
+      {
+        tokenIssuer: this.tokenIssuer,
+        catalogIdentityClient: this.catalogIdentityClient,
+        logger: this.logger,
+      },
+    );
+
+    const response: GcpIapResponse = {
+      providerInfo: { iapToken: result.iapToken },
+      profile,
+      backstageIdentity: prepareBackstageIdentityResponse(backstageIdentity),
     };
 
-    try {
-      const user = await verify();
-      if (user === undefined) {
-        this.logger.error('gcp iap proxy user returned undefined');
-        res.status(401);
-        res.end();
-        return;
-      }
-      const resolvedEntity = await this.options.identityResolutionCallback(
-        {
-          email: user.email,
-        },
-        this.catalogClient,
-      );
-      res.json(resolvedEntity);
-    } catch (e) {
-      this.logger.error('Verification failed with', e);
-
-      res.status(401);
-      res.end();
-      return;
-    }
-    res.status(200);
-    res.end();
-  }
-
-  start(): Promise<void> {
-    return Promise.resolve(undefined);
+    res.json(response);
   }
 }
 
+/**
+ * Creates an auth provider for Google Identity-Aware Proxy.
+ *
+ * @public
+ */
 export function createGcpIapProvider(
-  _options?: GcpIAPProviderOptions,
+  options: GcpIapProviderOptions,
 ): AuthProviderFactory {
-  return ({
-    logger,
-    catalogApi,
-    config,
-    identityResolver,
-  }: AuthProviderFactoryOptions) => {
+  return ({ config, tokenIssuer, catalogApi, logger }) => {
     const audience = config.getString('audience');
-    if (identityResolver !== undefined) {
-      throw new Error(
-        'Identity resolver is required to use this authentication provider',
-      );
-    }
-    return new GcpIAPProvider(logger, catalogApi, {
-      audience,
-      identityResolutionCallback: identityResolver,
+
+    const authHandler = options.authHandler ?? defaultAuthHandler;
+    const signInResolver = options.signIn.resolver;
+    const tokenValidator = createTokenValidator(audience);
+
+    const catalogIdentityClient = new CatalogIdentityClient({
+      catalogApi,
+      tokenIssuer,
+    });
+
+    return new GcpIapProvider({
+      authHandler,
+      signInResolver,
+      tokenValidator,
+      tokenIssuer,
+      catalogIdentityClient,
+      logger,
     });
   };
 }
diff --git a/plugins/auth-backend/src/providers/gcp-iap/types.ts b/plugins/auth-backend/src/providers/gcp-iap/types.ts
new file mode 100644
index 0000000000..5a8c3491fe
--- /dev/null
+++ b/plugins/auth-backend/src/providers/gcp-iap/types.ts
@@ -0,0 +1,96 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { JsonValue } from '@backstage/types';
+import { AuthHandler, AuthResponse, SignInResolver } from '../types';
+
+/**
+ * The header name used by the IAP.
+ */
+export const IAP_JWT_HEADER = 'x-goog-iap-jwt-assertion';
+
+/**
+ * The data extracted from an IAP token.
+ *
+ * @public
+ */
+export type GcpIapTokenInfo = {
+  /**
+   * The unique, stable identifier for the user.
+   */
+  sub: string;
+  /**
+   * User email address.
+   */
+  email: string;
+  /**
+   * Other fields.
+   */
+  [key: string]: JsonValue;
+};
+
+/**
+ * The result of the initial auth challenge. This is the input to the auth
+ * callbacks.
+ *
+ * @public
+ */
+export type GcpIapResult = {
+  /**
+   * The data extracted from the IAP token header.
+   */
+  iapToken: GcpIapTokenInfo;
+};
+
+/**
+ * The provider info to return to the frontend.
+ */
+export type GcpIapProviderInfo = {
+  /**
+   * The data extracted from the IAP token header.
+   */
+  iapToken: GcpIapTokenInfo;
+};
+
+/**
+ * The shape of the response to return to callers.
+ */
+export type GcpIapResponse = AuthResponse<GcpIapProviderInfo>;
+
+/**
+ * Options for {@link createGcpIapProvider}.
+ *
+ * @public
+ */
+export type GcpIapProviderOptions = {
+  /**
+   * The profile transformation function used to verify and convert the auth
+   * response into the profile that will be presented to the user. The default
+   * implementation just provides the authenticated email that the IAP
+   * presented.
+   */
+  authHandler?: AuthHandler<GcpIapResult>;
+
+  /**
+   * Configures sign-in for this provider.
+   */
+  signIn: {
+    /**
+     * Maps an auth result to a Backstage identity for the user.
+     */
+    resolver: SignInResolver<GcpIapResult>;
+  };
+};
diff --git a/plugins/auth-backend/src/providers/index.ts b/plugins/auth-backend/src/providers/index.ts
index 3f71dd2c26..a25d2ce8bc 100644
--- a/plugins/auth-backend/src/providers/index.ts
+++ b/plugins/auth-backend/src/providers/index.ts
@@ -27,6 +27,7 @@ export * from './oidc';
 export * from './okta';
 export * from './onelogin';
 export * from './saml';
+export * from './gcp-iap';
 
 export { factories as defaultAuthProviderFactories } from './factories';
 
diff --git a/plugins/auth-backend/src/providers/prepareBackstageIdentityResponse.ts b/plugins/auth-backend/src/providers/prepareBackstageIdentityResponse.ts
index 31df7a4cef..1de8ebb9b2 100644
--- a/plugins/auth-backend/src/providers/prepareBackstageIdentityResponse.ts
+++ b/plugins/auth-backend/src/providers/prepareBackstageIdentityResponse.ts
@@ -22,7 +22,9 @@ function parseJwtPayload(token: string) {
 }
 
 /**
- * Parses token and decorates the BackstageIdentityResponse with identity information sourced from the token
+ * Parses a Backstage-issued token and decorates the
+ * {@link BackstageIdentityResponse} with identity information sourced from the
+ * token.
  *
  * @public
  */
diff --git a/plugins/auth-backend/src/providers/types.ts b/plugins/auth-backend/src/providers/types.ts
index ecb466c768..0915bccc6c 100644
--- a/plugins/auth-backend/src/providers/types.ts
+++ b/plugins/auth-backend/src/providers/types.ts
@@ -200,13 +200,16 @@ export interface BackstageSignInResult {
 
 /**
  * The old exported symbol for {@link BackstageSignInResult}.
+ *
  * @public
- * @deprecated Use the `BackstageSignInResult` type instead.
+ * @deprecated Use the {@link BackstageSignInResult} instead.
  */
 export type BackstageIdentity = BackstageSignInResult;
 
 /**
- * Response object containing the {@link BackstageUserIdentity} and the token from the authentication provider.
+ * Response object containing the {@link BackstageUserIdentity} and the token
+ * from the authentication provider.
+ *
  * @public
  */
 export interface BackstageIdentityResponse extends BackstageSignInResult {
@@ -220,7 +223,8 @@ export interface BackstageIdentityResponse extends BackstageSignInResult {
  * Used to display login information to user, i.e. sidebar popup.
  *
  * It is also temporarily used as the profile of the signed-in user's Backstage
- * identity, but we want to replace that with data from identity and/org catalog service
+ * identity, but we want to replace that with data from identity and/org catalog
+ * service
  *
  * @public
  */
@@ -241,28 +245,32 @@ export type ProfileInfo = {
 };
 
 /**
- * type of sign in information context, includes the profile information and authentication result which contains auth. related information
+ * Type of sign in information context. Includes the profile information and
+ * authentication result which contains auth related information.
+ *
  * @public
  */
-export type SignInInfo<AuthResult> = {
+export type SignInInfo<TAuthResult> = {
   /**
    * The simple profile passed down for use in the frontend.
    */
   profile: ProfileInfo;
 
   /**
-   * The authentication result that was received from the authentication provider.
+   * The authentication result that was received from the authentication
+   * provider.
    */
-  result: AuthResult;
+  result: TAuthResult;
 };
 
 /**
- * Sign in resolver type describes the function which handles the result of a successful authentication
- * and it must return a valid {@link BackstageSignInResult}
+ * Describes the function which handles the result of a successful
+ * authentication. Must return a valid {@link BackstageSignInResult}.
+ *
  * @public
  */
-export type SignInResolver<AuthResult> = (
-  info: SignInInfo<AuthResult>,
+export type SignInResolver<TAuthResult> = (
+  info: SignInInfo<TAuthResult>,
   context: {
     tokenIssuer: TokenIssuer;
     catalogIdentityClient: CatalogIdentityClient;
@@ -271,23 +279,28 @@ export type SignInResolver<AuthResult> = (
 ) => Promise<BackstageSignInResult>;
 
 /**
- * The return type of authentication handler which must contain a valid profile information
+ * The return type of an authentication handler. Must contain valid profile
+ * information.
+ *
  * @public
  */
 export type AuthHandlerResult = { profile: ProfileInfo };
 
 /**
- * The AuthHandler function is called every time the user authenticates using the provider.
+ * The AuthHandler function is called every time the user authenticates using
+ * the provider.
  *
- * The handler should return a profile that represents the session for the user in the frontend.
+ * The handler should return a profile that represents the session for the user
+ * in the frontend.
  *
- * Throwing an error in the function will cause the authentication to fail, making it
- * possible to use this function as a way to limit access to a certain group of users.
+ * Throwing an error in the function will cause the authentication to fail,
+ * making it possible to use this function as a way to limit access to a certain
+ * group of users.
  *
  * @public
  */
-export type AuthHandler<AuthResult> = (
-  input: AuthResult,
+export type AuthHandler<TAuthResult> = (
+  input: TAuthResult,
 ) => Promise<AuthHandlerResult>;
 
 export type StateEncoder = (